linux - Pass a password to ssh in pure bash

Question

I want to pass a password to ssh using a bash script (Yes, I know that there are ssh keys that I could use, but this is not what I intend).

I found some solutions that were using expect but since it is not a standard bash tool I am wondering if I can do this using pipes.

Can someone explain to me, why exactly something like this:

echo "password
" | ssh somehost.com

or

ssh somehost.com <(echo "password
")

doesn't work? Is there any possibility to make it work? Maybe executing ssh as a different process, obtaining its PID and then sending a string directly to it?

Answer 1

You can not specify the password from the command line but you can do either using ssh keys or using sshpass as suggested by John C. or using a expect script.

To use sshpass, you need to install it first. Then

sshpass -f <(printf '%s
' your_password) ssh user@hostname

instead of using sshpass -p your_password. As mentioned by Charles Duffy in the comments, it is safer to supply the password from a file or from a variable instead of from command line.

BTW, a little explanation for the <(command) syntax. The shell executes the command inside the parentheses and replaces the whole thing with a file descriptor, which is connected to the command's stdout. You can find more from this answer https://unix.stackexchange.com/questions/156084/why-does-process-substitution-result-in-a-file-called-dev-fd-63-which-is-a-pipe